Characterization of Environmental Stress Cracking in Polymers Through a Modified Bent Strip Test Method

Background

The environmental stress cracking resistance (ESCR) of polymers is characterized most conveniently by the bent strip method standardized as ASTM D1693. The method has, however, suffered from poor reproducibility of the ESCR results.

Objective

In this study we propose modifications on the standardized method to reduce the variability of the ESCR results.

Methods

The notch is introduced to the specimens with the aid of automate testing machine instead of manual notching. The proposed method is then applied for a systematic investigation on the influence notch offset distance, notch inclination angle, notch depth on the environmental stress cracking behavior of polyethylene material.

Results

The results reveal interesting phenomenon that crack initiation occurs at the interior point between the endpoint and the middle of the notch, instead of at the middle point of the notch, where the maximum stress or strain is located. Finite element simulation has been conducted to elucidate root cause of this phenomenon. It has been found that the crack initiates at a point that is very close to the position of the maximum stress triaxiality, although the crack initiation position shifts slightly toward the position of the maximum stress or strain.

Conclusions

As a result, the crack initiation is controlled by the stress, strain and stress triaxiality, but stress triaxiality plays a dominant role in the initiation of environmental stress cracking.